# Frequently Asked Questions
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Active matrix liquid crystal display (LCD). A Liquid crystal based display technology that uses a switch at each pixel to create high resolution and fast response times. One type of LCD is known as thin film transistor (TFT) LCD, in which the switch used is a thin film transistor. Displays based on this technology range from as small as 1" diagonal up to 100" diagonal.
COB - Chip on Board. The LCD driver is epoxied onto the PCB and wire bonds are installed for connections to the IC. The chip plus bonding wires are covered with black epoxy as a seal.
COG - Chip-on-glass, a method of bonding driver integrated circuits (ICs) directly to the edges of active matrix liquid crystal displays (LCD's) for smaller packages, higher quality, and improved ruggedness. The driver IC is mounted upside down (flip chip) eliminating bond wires and interconnects. Reliability is improved due to reduction in interconnects.
COF - Chip on Flex. The LCD driver is incorporated into a flex connector, which is attached by a heat seal method to the contact edge of the LCD glass.
Organic light emitting diode (OLED), a flat panel display that uses organic compounds to emit light. OLEDs can be passive or active matrix. Passive matrix devices are easier to make, but not capable of full color or high resolution. Currently, active matrix devices use a poly-crystalline silicon thin film transistor (TFT) array, similar to low temperature poly-crystalline silicon (LTPS) active matrix liquid crystal displays (LCD's). There has been limited production to date because of short product lifetimes and differential aging rates of the OLED materials. This is also known as Organic EL.
These are the predecessors to active matrix liquid crystal displays (LCD's); these displays do not incorporate a thin film transistor (TFT) or switch at each pixel. As a result, they tend to have lower resolution, slower refresh rates, and poorer viewing angles than active matrix LCD's.
Transflective - A display that combines reflective and transmissive qualities. In dark ambient light environments, the back light can be used to provide light for the display. In bright ambient light environments, the back light can be switched off and the display used in reflective mode to save battery life. Most often used in PDAs and mobile phones. Good in sunlight and outdoor applications. Contrast ratio and brightness are decreased compared to transmissive type.
Transmissive - A display that uses a back light shining through the LCD to produce the image. Good in regular or dim lighting. Not for use in sunshine. Ambient light interferes with the back light, and “washes out” the display image. The light is created by a CCFL or light emitting diode (LED) back light, the switching is provided by the thin film transistor (TFT) array, and the color is provided by the color filter.
The angle at which the viewer must be in comparison to the screen, in order to see the image on a display. For example, a 0° horizontal viewing angle is directly in front of the display and a 90° horizontal viewing angle is directly to the side. Emissive displays show the same brightness and color regardless of viewing angle, however, rear projection displays and transmissive displays can show some differences in color, brightness, and gray scale, with the most difference being noticed at the steepest viewing angles.
For LCD, Wide Operating Temp Range = -20C to +70C. Regular Operating Temp Range = 0C to +50C. LCD have very poor temperature performance inherent to the technology. By comparison, wide operating temp range for semiconductors is -55C to +125C.